1. Field of the Invention
The present invention relates to an image building apparatus of the type in which a required image is built on a sheet of printing medium by transferring coloring agent on a strip of ink donor medium onto the printing medium by means of a printing head and more particularly to improvement of an image building apparatus of the above-mentioned type in which the ink donor medium is spanned between two cores.
2. Description of the Prior Art
For instance, a thermal transferring type image building apparatus will be noted as one of transferring type image building apparatuses. The thermal transferring type image building apparatus uses ink donor medium in the form of thermal transfer ribbon on which a thermally fusible or thermally sublimable coloring agent is coated and the recording head is generally constructed in the form of a thermal head. Since this type of image building apparatus is designed and constructed with relatively small dimensions at an inexpensive cost and with generation of noise reduced remarkably and moreover since plain paper can be used as a printing medium, it is increasingly put in practical use in recent years not only as an output recorder for a computer, word processor or the like apparatus but also as a copying apparatus.
However, the conventional image building apparatus of the early-mentioned type in which transferring is effected by fusing ink on the thermal transfer ribbon by heating and then transferring molten ink on a sheet of recording medium has a problem that the content of transference is left behind on the thermal transfer ribbon in the form of negative image. For the reason, there is a necessity for keeping the content of the transference secret in some case.
For instance, in the case where copying service is rendered at a copy shop, a requirement is raised from a client that he wants to carry back the used thermal transfer ribbon after completion of transferring operation for the purpose of keeping the content of transference secret. To meet the requirement the copy shop usually uses a new thermal transfer ribbon to carry out subsequent transferring and gives the used thermal transfer ribbon to him after completion of transferring operation at a reasonable cost. However, in the case where copying service is rendered for a small number of sheets of printing medium there appears a problem that the used thermal transfer ribbon is handed over to him with a considerably long part of the thermal transfer ribbon left unused, resulting in the selling price of the used thermal transfer ribbon becoming expensive.